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scratch
scratch

Posted: Fri Sep 13, 2013 11:34am

Post Subject: Can I plumb skin tanks in series?

Hi We have a 15m widebeam powered by a Barrus Shire 45. In normal usage (top part of upper tidal Thames and non-tidal Thames) everything's fine. Temperature gauge seems to be around the 80-85 degree mark under typical usage once everything's warmed up. Yesterday we went downstream to the lower sections of the tidal Thames. Everything went well. Our boat bounced around the rougher sections of the Thames without issue. Indeed, I was amazed at how well she handled the chop thrown up around the bridges and by some of the larger passenger craft. It was fun. The not so amusing part was when we came about to go back to our short term mooring (which we'd gone past in the name of further exploration). Pushing against the river and tidal flow, we were still going backwards at 1,900 RPM. Increasing revs (2,300 RPM) had us creeping forward – but the engine temperature started to rise alarmingly. It hit 95 degrees quite quickly and kept on inching upwards. At 97 degrees I backed off the throttle slightly (2,100 RPM). The temperature dropped back to 95 degrees and remained constant. Eventually we made our mooring. But it was sloooow going. Our engine has been run for periods of time at her full 2,800 RPM without any significant issue. (Per the Barrus Shire operating manual: "It is recommended that the engine is run at full load for 15 minutes (maximum revs, in gear) every 50 hours"). But of course this has been under circumstances where I can back off the throttle when the temperature starts to become an issue (a fact that I'm only fully acknowledging as I type this). We will be doing similar trips to the lower tidal Thames in the future. Not everyday but as occasional treats to ourselves – and I'd like to have our full compliment of ponies on hand to help out if need be. We have a second skin tank for the genset. It occurs to me that we could plumb this in in series with the drive engine's skin tank to double the cooling area. Is this a really stupid idea? The engine and genset rarely run at the same time and I fail to see why they can't share the same cooling circuit. Perhaps not best practice but can any harm come from it? Perhaps the most significant issue is that during more normal usage the engine will struggle to get up to temperature (ironic huh). However, putting a thermostatic valve in to bring the second skin tank on line when the temperature hits 90 degrees may be an option? What say the learned members of this forum? I look forward to your replies. All the best Scratch. PS I accept that a 15m widebeam with a 45hp engine is not the best tool for the lower reaches of the Thames. However, she's perfect for the upper reaches and non-tidal sections of the Thames – her typical stomping ground. Life's a compromise. Here's one of them.

scratch
scratch

Posted: Fri Sep 13, 2013 11:52am

Post Subject: Can I plumb skin tanks in series?

And again, tidied up (hopefully) to account for the vagaries of the forum... Hi We have a 15m widebeam powered by a Barrus Shire 45. In normal usage (top part of upper tidal Thames and non-tidal Thames) everything's fine. Temperature gauge seems to be around the 80-85 degree mark under typical usage once everything's warmed up. Yesterday we went downstream to the lower sections of the tidal Thames. Everything went well. Our boat bounced around the rougher sections of the Thames without issue. Indeed, I was amazed at how well she handled the chop thrown up around the bridges and by some of the larger passenger craft. It was fun. The not so amusing part was when we came about to go back to our short term mooring (which we'd gone past in the name of further exploration). Pushing against the river and tidal flow, we were still going backwards at 1,900 RPM. Increasing revs (2,300 RPM) had us creeping forward - but the engine temperature started to rise alarmingly. It hit 95 degrees quite quickly and kept on inching upwards. At 97 degrees I backed off the throttle slightly (2,100 RPM). The temperature dropped back to 95 degrees and remained constant. Eventually we made our mooring. But it was sloooow going. Our engine has been run for periods of time at her full 2,800 RPM without any significant issue. (Per the Barrus Shire operating manual: "It is recommended that the engine is run at full load for 15 minutes (maximum revs, in gear) every 50 hours"). But of course this has been under circumstances where I can back off the throttle when the temperature starts to become an issue (a fact that I'm only fully acknowledging as I type this). We will be doing similar trips to the lower tidal Thames in the future. Not everyday but as occasional treats to ourselves - and I'd like to have our full compliment of ponies on hand to help out if need be. We have a second skin tank for the genset. It occurs to me that we could plumb this in in series with the drive engine's skin tank to double the cooling area. Is this a really stupid idea? The engine and genset rarely run at the same time and I fail to see why they can't share the same cooling circuit. Perhaps not best practice but can any harm come from it? Perhaps the most significant issue is that during more normal usage the engine will struggle to get up to temperature (ironic huh). However, putting a thermostatic valve in to bring the second skin tank on line when the temperature hits 90 degrees may be an option? What say the learned members of this forum? I look forward to your replies. All the best Scratch. PS I accept that a 15m widebeam with a 45hp engine is not the best tool for the lower reaches of the Thames. However, she's perfect for the upper reaches and non-tidal sections of the Thames - her typical stomping ground. Life's a compromise. Here's one of them.

Tony-B
Tony-B

Posted: Fri Sep 13, 2013 1:32pm

Post Subject: Can I plumb skin tanks in series?

First of all you have no need to mess about with a thermostatic valve. The speed of warm up is governed by the engine thermostat and calorifier size if it is fed from the engine side of the thermostat. The warm up time should not alter. The only thing I can see that might complicate putting the two tanks in series is the relative pressure cap settings on the main engine and generator. If they both have the same nominal setting then in theory it should be fine but I very much doubt the settings are in any way accurate so one probably has a slightly lower setting than stated. In this case it would leak coolant all the time the engine was running. For the use you propose I think it may be worth getting a higher pressure cap and fit it to the generator. The engine cap would do the job for the generator if both are using the skin tanks. The increase in coolant volume would also cause an increase in the expansion volume so you might have to fit a larger coolant header tank. I am very unsure of what will happen if you tried to run the generator and engine at the same time. You might get an overheat. Depending upon pipe layout it may also make bleeding the system more of a pain. Tony Brooks

scratch
scratch

Posted: Sat Sep 14, 2013 10:35pm

Post Subject: Can I plumb skin tanks in series?

Hi Tony Many thanks for the reply – much appreciated. WIth respect to the pressure cap settings - excellent point and one which had escaped me completely. Agreed. Fit a higher pressure cap to the generator. The expansion tank side of things – prepared for this. The original engine expansion tank is a... peanut. Minute. An insult to expansion tanks. When I bought the boat, there was a 2 litre coke bottle catching the excess once things had warmed up and one had to refill the expansion tank once everything cooled down. (As an aside, I spent some time searching for an air trap thinking that it was air expansion causing the issue. Eventually I researched the expansion rate of water and realised that what I was seeing was simply due to the expansion of the water in the skin tank. Somewhat unbelievable that such a silly little expansion tank had been fitted in the first place). Anyway, the overflow tank I fitted probably is big enough but linking up another would take but half an hour. Running both the generator and engine at the same time is rare - and then usually for a very limited period of time. It'll be interesting to see what happens! One mild concern is the ability of the water pump to push water through two skin tanks. You don't think this would be a major concern? (I'd have thought we'd be OK. Pipes are 2" diameter and runs are clear of any constrictions). Anyway, all sounds good. A winter project! Thanks Simon

Tony-B
Tony-B

Posted: Sat Sep 14, 2013 10:53pm

Post Subject: Can I plumb skin tanks in series?

Sorting out undersized skin tanks is very common and it often involves either another tank in series or some pipework on the outside of the swim, also in series so I do not think there will be a problem. Tony Brooks

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